Control for electric motors



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Patented June 28, 1949 2,474,595 CONTROL FOR ELECTRIC MOTORS Max C. Richardson, Portland, Oreg., assignor to Iron Fireman Manufacturing Company, Portland, Greg.

Application October 10, 1944, Serial No. 558,044

s claims. 1

My invention relates to power circuits and more particularly to the control of power circuits.

My invention comprises a novel power control system in which three functions are uniquely combined to assure the satisfactory operation of the system.

Although my invention is equally applicable to power circuits in which the conveying medium is a luid, for simplicity ci exposition I will describe the invention as applied to an electric power circuit. More specifically I will describe my invention as applied to an electric power circuit used to control the heat to be supplied by an automatic fuel burner.

With an automatic electric control system for.

. and open a circuit when there is respectively a need or a surplus of heat. Also, it is common practice to use a timer or program type of switch to perform a similar function.

In certain cases it has also been found desirable, after a burner has been started by a time or condition responsive switch, to make use of a switch responsive to a second condition to hold the burner in operation until a desired change has occurred in this second condition.' In certain other cases it has been found desirable to limit the time that a burner is allowed to operate without causing a specified condition change. The so-called outllre -control elements well known in the automatic coal-burning and the automatic oil burner arts illustrate the desirability of this function.'

It is an object of my invention .to provide a system in which the above three control functions are uniquely combined tol assure the. most satisfactory operation of the system.

Other objects and advantages will become apparent to those skilled in the art of power control by reference to the further description, drawings, and claims hereof.-

Referring now to the drawings, the iigure is a schematic drawing showing my invention by the use of conventional symbols. In the gure line and 26 are considered as electrical supply lines assumed to be connected to an electrical generator (not shown). 2| is an electric motor used to drive the fuel feederfof an automatic burner. |4 is the actuating coil of an electrical relay which, when energized, causes the armature 41 to lift the insulating bar 48 which carries the two conducting bridges 32 and 24 into contact respectively with the two pairs of contacts 3|, 33

. and y34.

and 23, 25. When coil I4 is deenergized armature 41 drops and bridges 32 and 24 fall away from their respective associated contacts. Lines 21 and 29 connect the transformer primary coil 28 with the electrical supply lines 2B and 26. 4 is the stationary contact of a circuit opening switch of which 5 is the moving contact carried by a bi-metallic blade 6 which will flex to open contacts 4, 5 when heated by electric current flowing through the nearby resistance type heater 38. An insulating blade 43 secured to bimetal 6 is engaged by ledge 44 of pendulum latch 45 supported on pin 4t whenever bimetal 6 opens contacts 4, 5. Latch r45 must then be manually pushed away from blade 43 to allow contacts 4, 5 to close.

Ii is a circuit closing switch shown as a conventional bimetal space thermostat with stationary contact 9 and movable blade I0. However in actual practice switch Il might be any type of circuit closing switch. At 4I is shown a second condition responsive switch shown as a blade 40 actuated by a bimetal coil to connect line 42 with lines 34 and 31 through contacts 35 and 36.

In the figure it is seen that we have an energizing circuit in which a source of power 2 is connected through line I1 to a circuit opening switch 6 which is connected with a line from terminal 1 to terminal 9 to a circuit closing switch I I and on through line I8 to a power absorbing relay coil i4 from which line I9 closes the circuit to transformer secondary 2.

It is seen on examination of. the figure that when contacts 4 and 5 of circuit opening switch 6 are separated no power can flow in any circuit shown.

When contacts 4, 5 are closed and contacts 9, l0 are closed power will flow in the circuit and the fuel feed motor will be energized through relay elements 23,24, 25. At the same time elements 3|, 32, 33 will close to connect lines 30 Condition responsive switch 4l would in our automatic burner illustration be so located as to be responsive to combustion temperature and would be closed at low combustion temperatures and open at higher combustion temperatures. Therefore, when switch closes to energize relay I4 and start fuel feed motor 2|, switch 4| will usually be closed and a holdingcircuit will be7 established from terminal I2 on one side of switch II through'switch 4| line 34, elements 3|, 32, 33, and line 30 to terminal 8 on the other side of switch |I. This maintaining circuit will try to keep the fuel feed motor running until the 3 temperature of combustion as felt by element 4I changes to open the circuit through elements 35, 40.

Also, when switch Il is closed and switch 4I is closed, a de-energizing circuit will be established from terminal l2 through line 42 through contact elements 40, 36, line 31, switch actuator 38, and line 39 to terminal i6 and power will ow from source 2 to switch actuator 38. Switch actuator 38 will have been adjusted to cause contacts 4. 5 to open at a desired time delay after 38 is energized. Thus if the combustion temperature rises in a normal way switch 4i will open before switch 6 and switch 6 will not open, but if the rise in combustion temperature is abnormally clelayed, switch 5 will open before switch 4i opens and the system will be shut down completely.

The condition of the control system as shown in the ligure is a normal operating condition after a period of motor operation and wherein the motor operation was initiated by a requirement to which switch H is subject and wherein the motor operation was stopped by the satisfaction of the requirement to which switch H is subject. Switch 40 is shown open because during the operation of the motor the requirement to which switch 4U is subject was satisfied. Contacts 4 and 5 remain closed because during the operation of the motor the requirement to which switch 40 is subject was satisii'ed is iess than the delay period of element 6 and its operator 38.

I claim:

1. The combination in a motor control system of a motor circuit, an energizing circuit, hold-1 ing circuit, and a de-energizing circuit, said motor circuit comprising in series, electric supply lines, an electromagnetic motor starting switch and said motor, said energizing circuit comprising in series a source of electric power, the operating coil of said electromagnetic motor starting switch, a circuit opening means and a circuit closing means, said holding circuit being in parallel with said circuit closing means and comprising in series means for opening said holding circuit when said energizing circuit is opened and means for de-energizing said motor in response to a condition when said circuit closing means is open, said de-energizing circuit being in parallel with the operating coil of said electromagnetic switch and comprising in series a time delay means for operating vsaid circuit opening means and means for opening said de-ener gizing circuit in response to a condition.

2. In a motor control system, in combination, a circuit for causing said motor to be energized, a holding circuit, and a cie-energizing circuit, said energizing circuit including a source of electric power, a circuit opening means and a circuit closing means, said de-energizing circuit being a series circuit including said source of power, said circuit opening means, said circuit closing means, a condition responsive circuit opening means and meansfor operating said circuit opening means, said holding circuit being in parallel with said circuit closing means and including in series a condition responsive circuit closing met tis and means for closing said holding circuit when said motor is energized if said condition responsive cir-cuit closing means is closed.

3. In a motor control system, in combination, a circuit for causing said motor to be energized, a holding circuit and a de-energizing circuit, said energizing circuit including a source of electric power, a circuit opening means and means for closing said energizing circuit in response to requirement, said. cle-energizing circuit being a series circuit including said source of power, said circuit opening means, said energizing circuit closing means a condition responsive circuit closing means and time delay means for operating said circuit opening means, said holding circuit being in parallelwith said energizing circuit closing means and including in series a condition responsive circuit opening means and means for opening said holding circuit when said motor is deenergized if said condition responsive circuit opening means is closed.

MAX C. RICHARDSON.

REFERENCES CITED The following referenices are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,669,386 Williams May 8, 1928 1,707,194 Shivers Mar. 26, 1929 1,707,195 Shivers Mar. 26, 1929 2,157,710 Lake May 9, 1939 2,300,838 Dicke Nov. 3, 1942 2,305,507 Wilson Dec. 15, 1942 2,319,774 Rankin May 18, 1943 2,333,432 vLum Nov. 2, 1943 

